Insight into the preparation of poly(vinylidene fluoride) membranes by vapor-induced phase separation

Improving Liquid Entry Pressure of Polyvinylidene Fluoride (PVDF) Membranes by Exploiting the Role of Fabrication Parameters in Vapor-Induced Phase Separation VIPS and Non-Solvent-Induced Phase Separation (NIPS) Processes

“…In general, VIPS membranes, irrespective of applied RH, show a much higher CA (>125 • ) than the NIPS membrane (CA = 90.74 • ), as shown in Table 2. This finding regarding VIPS morphology was also reported elsewhere [14]. When calculating the LEP of membranes prepared using both processes, they all range from 103 to 107 kPa, which makes the membranes vulnerable to wetting.…”

Design of near-superhydrophobic/superoleophilic PVDF and PP membranes for the gravity-driven breaking of water-in-oil emulsions

“…The overall porosity remains the same for all PVDF membranes, in the range 70-75%.In the case of VIPS, these values are consistent with earlier studies [34,37] . Less examples are available in literature for accurate comparisons of our LIPS membranes because water is often the preferred coagulant.…”

“…So, the dissolution temperature of PVDF was set to 50 °C and the RH to 70%. We could have further increased the size of nodules, by decreasing the level of relative humidity or increasing the dissolution temperature, but it was shown that hydrophobicity did not increase that much and mechanical properties decreased, accordingly to a previous work showing the close relationship between the size of the nodules and the mechanical properties of the membranes [34] . Therefore, a balance between hydrophobicity and mechanical behavior had to be found.…”

“…However, gravity force acting on the emulsion cannot be neglected. Consequently, we evaluated the modulus of elasticity of membranes using a tensile tester as tests in tension are currently commonly performed in studies on polymer membranes such as PVDF membranes [34,37] and we planned to challenge the values obtained against those reported in literature for similar membranes that were then used in filtration processes with a transmembrane pressure other than static gravity head. Results of Table 1 reveal that the strongest and the stiffest PVDF membranes are the VIPS membrane (E = 14.8 ± 1.1 MPa, TS = 0.43 ± 0.05 MPa) and the LIPS membrane (E = 16.9 ± 1.0 MPa, TS = 0.50 ± 0.03 MPa).…”

“…Modulus of elasticity of our VIPS membranes compares to that obtained with a PVDF membrane cast from a solution dissolved at 45 °C, found to be 15 ± 9 by Li et al . , [34] . It also presented a tensile strength at break in the same range as that reported by Peng et al .…”